Container

ABSTRACT

A container ( 1 ) particularly for food products comprising a metal can body ( 2 ) and a combination of a ring ( 12 ) and a foil membrane ( 14 ), the combination being attached to the can body, in which the ring is made of a plastics material, wherein the inside diameter of the plastic ring is no less than the inside diameter of the can body away from the attachment location of the ring on the can body.

TECHNICAL FIELD

This invention relates to a container. In particular, it relates to acontainer which comprises the combination of a can body for productssuch as food, and a closure element. The invention also includes amethod of forming the combination of can body and closure element.

BACKGROUND ART

Cans for the packaging food are typically of a two or three piece form,comprising a tubular can body, either cylindrical or irregular/polygonalin cross-section, with a base and closed by a can end, diaphragm, film,screw top or other closure. The base may be integral with the can bodyso as to form a so called two-piece can body, or the can body may beformed from a tube of sheet metal with the edges of the sheet metaljoined by a welded side seam, which is then closed at both ends to forma three-piece can.

Typical food cans which are closed by a can end, have sealing compoundin the curled edge of a cover hook portion of the can end in order toprovide a tight hermetic seam, usually known as a double seam due to thetwo thicknesses of metal in the seam—one from the can body and the otherfrom the can end. A problem with a three piece can body is that thewelded side seam provides an irregular sealing surface for seaming. Thesealing compound needs to be precisely and uniformly placed so that theresultant ring of sealing compound within the seam has the right width,thickness and position to ensure that the seam has the requiredtightness. Double seam technology is a precise art, which relics onnumerous factors for seam integrity, of which the sealing compound isone important feature.

Cans for other products may use different closure arrangements; forexample, a peelable foil is typically seated on an intermediate metalring which, in turn, is seamed to the can body. Such can and ringcombinations are expensive to manufacture as the central disc from thering element is generally scrapped, leading to material wastage.Proposals such as those described in

Patent Citation 0001: EP 1029613 A (IMPRESS GMBH & CO). 2000-08-23.

and

Patent Citation 0002: WO 2005063587 A (CROWN PACKAGING TECHNOLOGY INC).2005-07-14.

avoid wasting the centre of the ring, but include additionalmanufacturing stages which, in turn, involve extra process time and/orcapital equipment costs.

Patent Citation 0003: EP 0819086 B (GRABHER, WERNER). 1998-12-23.

describes a semi-finished can which is open at one end and closed at itsother end by a cup-shaped foil membrane. The sidewall of the foil cupextends in the direction of the can axis and is bonded directly to theinside of the can wall. The foil may extend over the can body edge,which has been formed into a hook or curl. Although inexpensive tomanufacture, unfortunately when cans closed in this way are stacked, thepressure of the upper can bears directly onto the foil, risking damageto the foil. In addition, the foil is bonded to the can body over a sideseam which presents an irregular sealing surface as described above.

Another problem with

Patent Citation 0004: EP 0819086 B (GRABHER, WERNER). 1998-12-23.

is that the container is unsuitable for use with foods which generateinternal positive pressure within the can body during processing as thistends to peel the foil from off the sidewall of the container.

This invention seeks to overcome the problems of EP 0819086 B whilststill providing a container that is less expensive and wasteful tomanufacture than the ring and peelable foil membrane closures describedabove.

DISCLOSURE OF INVENTION

This invention seeks to provide a can body and closure element forclosing by a variety of closure panels (can end, diaphragm, disc etc.)at a reduced cost in comparison with traditional peelable closures.

Accordingly, a first aspect of the invention provides a containercomprising:

a metal can body, anda combination of a ring and a foil membrane, the combination beingattached to the can body,in which the ring is made of a plastics material,characterised in that the inside diameter of the plastic ring is no lessthan the inside diameter of the can body away from the attachmentlocation of the ring on the can body.

Use of a plastic ring is more economical than using a metal ring fromwhich the centre is generally discarded. The bond between the ring/foilmembrane combination and the can body provides a strong connection togive a hermetic seal. Furthermore, the ring/foil membrane combinationcovers any weld (for example, a welded side seam in the sidewall of a 3piece can) and the plastic ring supports any container stacked on top,without risk of damage to the foil membrane.

Ensuring that the inside diameter of the plastic ring is no less thanthe inside diameter of the can body away from the attachment location ofthe ring on the can body is beneficial in maximising the openingaperture of the container and in enabling full release of product fromthe container. The can body may have a generally cylindrical profile,i.e. with a straight or tapered sidewall. In such an embodiment, thering may be retained by contact between the ring and the exteriorsurface of the can body; conveniently, retention of the ring on the canbody is enabled by the ring having an outer peripheral wall and a hookportion as described below.

Preferably however, the edge of the can body to which the ring/foilmembrane combination is attached comprises an expanded portion, all orpart of the ring locating within the expanded portion, the insidediameter of the ring being no less than the inside diameter of theunexpanded portion of the can body. Usually the height of the ringcorresponds to the axial length of the expanded part of the can body.Consequently, the inner sidewall of the ring extends smoothly into theinner sidewall of the can body. This is beneficial in enabling fullrelease of product from the container and is particularly useful forsolid or semi-solid food products, such as cooked meats, thick soups orpet food

In one embodiment, the ring is bonded permanently to the can body andthe foil membrane is bonded peelably to the plastic ring. The ring maybe formed from a conventional thermoplastic polymer, such aspolypropylene. The bonding between the ring and the can body may beenhanced by selection of the coating on the can body; for example, afilm of heat sealable lacquer may be applied at the interface betweenthe ring and the can body or be precoated onto the can body and/or thering. The ring may be heat sealed to the can body, for example usinginduction heating, with the application of heat causing the heatsealable lacquer to form a bond between the ring and the can body. Whenusing induction heating to bond the ring to the can body, the foilmembrane is typically peelably bonded to the ring subsequent to thebonding of the ring onto the can body, thereby ensuring that any metalin the foil membrane will not interfere with the induction heatingprocess. The resulting container is more easy to open by peeling thanthat of EP 0819086 B, which is not in peel mode for opening.

In a preferred embodiment, the ring is directly bonded to the sidewallof the can body. The plastic ring may be made from a thermoplasticpolymer; it has been found beneficial for the plastic ring to comprisepolypropylene or modified polypropylene. The ring may then be placed inposition on the can body and suitable heating means applied (forexample, induction heating). The action of the heating causes thesurface of the ring itself to directly bond with the surface of the canbody, even when the can body surface includes protectivelacquers/coatings (for example, epoxy-based coatings). Advantageously,the modified polypropylene comprises polypropylene grafted with maleicanhydride. Such a modified polypropylene has been found to form a strongbond with conventional lacquers of the type commonly used on metal canbodies to protect the metal substrate of the can body, such asepoxy-based lacquers. Polypropylene is a non-polar material, whereas thelacquers used to protect the metal substrate of a can body (e.g.epoxy-based lacquers) are often polar materials. The addition of maleicanhydride improves the ability of the non-polar polypropylene of theplastic ring to bond with polar lacquers provided on the can body.

The can body may comprise a curl or flange, and the ring may include ashoulder which is adapted to extend over the can body curl/flange.Preferably, the shoulder extends into an outer peripheral wall whichdepends from the shoulder over the outside of the can body curl/flange.Advantageously, the outer peripheral wall comprises a hook portion so asto clip over the can body curl/flange to retain the ring on the canbody. The hook portion is useful for retaining the ring in position onthe can body if the ring is to be fixed onto the can body by inductionheating (or other means involving application of heat to the ring),because it compensates for any thermal expansion or contraction of theplastic ring relative to the metal can body.

Conveniently, the shoulder includes a portion which extends upwardly toprovide a rim for handling and tab protection. Preferably, the base ofthe container and the rim are formed such that the base of a firstcontainer of the present invention may be located within the rim of asecond container of the present invention, thereby enhancing the abilityto stack the containers on top of each other.

In one embodiment, the ring's shoulder is provided with a substantiallyflat bonding surface, and the foil membrane is bonded to this flatsurface. In an alternative embodiment, the ring is provided with abonding surface inclined downwardly at an angle of up to 60°, and thefoil membrane is bonded to this inclined surface. The provision of suchan inclined bonding surface has been found to enable retort processingof the container. When subject to internal positive pressure duringprocessing, the foil would expand outwardly to form a curved profile.The inclined bonding surface ensures that the foil membrane is mainlyloaded in shear rather than in peel when subject to internal positivepressure, thereby inhibiting loss of seal between the foil membrane andthe plastic ring. More preferably, the bonding surface is insteadinclined downwardly at an angle of up to 45°.

The foil membrane usually includes a tab for gripping to peel the foilmembrane from the ring. Ideally, this tab is situated towards one edgeof the foil in order to reduce peel force requirements.

Alternatively, the foil membrane may be formed in the shape of a cup(i.e. cup-shaped) and the sidewall of the foil cup bonded to the innersidewall of the ring. In this embodiment, it is beneficial for any tabto be situated away from the sidewall of the cup-shaped foil to assistin peelable removal of the foil.

In a second aspect of the present invention, there is provided a methodof forming a container, the method comprising:

forming a metal can body;fixing a ring of plastics material permanently to the can body, theinside diameter of the plastic ring being no less than the insidediameter of the can body away from the attachment location of the ringon the can body; andbonding a foil to the ring such that, in use, the foil may be peeledfrom the ring for dispensing a product from the container.

Preferably, the can body is formed with a radially expanded portion atone end of the can body, and the plastic ring is fixed permanently tothe can body such that all or part of the ring is located within theexpanded portion.

Alternatively, the steps of fixing the ring and bonding the foil may bereversed such that the foil is first bonded to the ring and thecombination of ring and foil is subsequently fixed to the can body.

According to a third aspect of the present invention, there is provideda container comprising:

a metal can body, anda combination of a ring and a foil membrane, the combination beingattached to the can body,in which the ring is made of a plastics material,characterised in that the ring/foil membrane combination comprises apermanent bond between the membrane foil and the ring, and the foil ispeelably bonded to the inside of the can body sidewall.

In this aspect of the invention, the ring may include a tab or ring pullfor removing the ring and foil together as a single entity from thecontainer. The relative rigidity of the plastic ring compared to thefoil membrane may enable the container to be recloseable by locating thering/foil membrane combination back onto the can body.

This aspect of the invention may also incorporate one or more of thefeatures described above for the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way ofexample only, with reference to the drawings, in which:

FIG. 1 is a side section of a first embodiment of a container accordingto the invention;

FIG. 2 is a perspective view of the container of FIG. 1;

FIG. 3 is a side section of a second embodiment of a container accordingto the invention;

FIG. 4 is a perspective view of the container of FIG. 3;

FIG. 5 is side section of a third embodiment of a container according tothe invention;

FIG. 6 is a perspective view of the container of FIG. 5;

FIG. 7 is a side section of a fourth embodiment of a container accordingto the invention;

FIG. 8 is a side section of a fifth embodiment of a container accordingto the invention; and

FIG. 9 is a perspective view of the container of FIG. 8.

MODE FOR THE INVENTION

FIGS. 1 and 2 show a container 1. The container 1 is of a so-called“three piece” type, comprising a cylindrical can body 2 that is closedat its lower end by a conventional closure 3. The closure 3 is joined tothe can body 2 by a double seam 4. The can body 2 is radially expandedby an amount ‘a’ (in this example, approximately 2 mm) at its upper endto provide a stepped portion 5 and terminates in a flange or curl 6.

The can body 2 may be formed from a metal sheet which is coated with alacquer, polypropylene being dispersed within the lacquer. The metalsheet may then be formed into a cylinder (for example, by welding) toprovide the can body. The welded side seam thus formed on the can bodyis generally separately coated with a similar internal lacquer or with apolypropylene powder. Alternatively, the metal sheet could be coatedwith a conventional lacquer and a specific lacquer, such as oneincluding a dispersion lacquer, used only for coating that part of thecan wall and weld which is to contact the plastic ring 12.

The upper end of the can body 2 is closed off by a closure 10. Theclosure 10 includes a plastic ring component 12, and a diaphragm or foil14 with a peripheral tab 16 for opening. The plastic ring 12 is mouldedinto a first annulus 18 that is substantially cylindrical and shaped tobe seated within the stepped portion 5. In the embodiment shown, theplastic ring 12 has an internal diameter which is the same as that ofthe unexpanded portion of the can body 2. This provides a smoothtransition from i) the inner sidewall of the unexpanded portion of thecan body 2 to ii) the inner sidewall of the plastic ring 12, therebyoptimising product release. However, alternative embodiments may havethe plastic ring 12 having an internal diameter which is greater thanthat of the can body 2 beneath the stepped portion 5. In either case,the plastic ring 12 does not impede the release of product from thecontainer 1, but instead promotes full product release. The plastic ring12 is also typically of either polypropylene for bonding to apolypropylene dispersion in the internal can body coating, or modifiedpolypropylene for bonding to conventional lacquers.

The annulus 18 of the plastic ring 12 extends radially outwardly into aflat shoulder portion 20 which, in turn, extends outwardly anddownwardly into a retention portion 22 and upwardly into a rim 24. Theplastic ring 12 may also be shaped (for example, with a hooked portion)so as to be snapped into position around the can body flange or curl 6and thereby hide any exposed metal of the flange or curl. The annulus 18is permanently bonded to the can body, for example by induction heating.The bonded region may also include the curl or flange 6.

The foil 14 is bonded to the flat shoulder portion 20 which forms asealing surface of 1.0 to 2.5 mm in width. The centre region of the foil14 as shown in FIG. 1 is domed inwardly due to negative pressure(so-called “vacuum”) within the container following filling orprocessing.

The container 1 of FIGS. 1 and 2 is typically formed in two separatestages. In one stage, the can body 2 has the flange or curl 6 formedaround the periphery to which the plastic ring 12 is to be bonded, andthen the upper region of the can body 2 is radially expanded to form thestepped portion 5. The plastic ring 12 is bonded to the can body 2 byinduction heating, and the foil 14 then fixed to the plastic ring. Thecontainer 1 is filled through its bottom end and the closure 3 seamedonto the filled container. In this method, the foil 14 does notinterfere with the induction heating process and the induction heatingdoes not interfere with the peelable bond between the foil 14 andplastic ring 12.

The example of FIGS. 3 and 4 is similar to that of FIGS. 1 and 2 butincludes a shoulder portion 21 which slopes downwardly from thehorizontal by an angle α (in this example, 20°). Downwardly extending or“barometric” shoulders are preferred for containers in which the liddingmaterial is deflected by in-can pressure during processing of the foodproduct in the container and enables use in reel and spiral retorts (orsimilar processes). By inclining the shoulder portion 21 downwardly, theangle α becomes greater than the angle subtended by the extremity of thelidding material in its outwardly domed position when subject topositive internal pressure. As a result, the sealing surface ispredominantly loaded in shear rather than in peel, which effectivelydoubles the burst pressure performance from that of containers with flatshoulders (such as that of FIGS. 1 and 2) which would be loaded in peelmode when subject to positive internal pressure. For barometricshoulders, preferred bonding surface angles α are up to 45° to givesufficient dome size, although in theory angles α of up to 60° arepossible.

Although the centre region of the foil 14 of FIGS. 3 and 4 has beenshown with a plain surface, decoration for customisation or beading forimproving barometric performance may be used to allow for movement ofthe foil 14 whilst avoiding foil wrinkling.

This embodiment may be formed in the same way as that of FIGS. 1 and 2.Of course, either of these two embodiments could use a container drawnfrom a blank of sheet metal to form a sidewall and integral base (i.e.no welded side seam), in which case the plastic ring 12 and foil 14 maybe formed as one component which is subsequently bonded to the can body2 after filling. Alternatively, the ring 12 may first be bonded to thecan body 2, the can filled and the foil 14 then bonded to the plasticring.

In the alternative container shown in FIGS. 5 and 6, like features ofthe can body 2 are given the same reference numerals as in FIGS. 1 to 4.The plastic ring 12 of this embodiment comprises a shoulder 13 whichextends over the edge of the can body (here shown as a curl 6, althoughthe edge may be unshaped or a simple flange) and the annulus 18 isseated against and permanently bonded to the inner wall of the can body2 in the same manner as the embodiments of FIGS. 1 to 4. However, inFIGS. 5 and 6, the foil 14 is peelably bonded to the inner wall of theplastic ring 12, rather than to a flat or downwardly inclined portion ofthe ring. In this embodiment, the foil 14 defines a cup-shape profile.This avoids the problems of direct welding of foil over a weld margin asarises in processes such as that described in

Patent Citation 0005 EP 0819086 B (GRABHER). 1998-12-23.

Tab 16 of FIGS. 5 and 6 is bonded to the central part of foil 14. Thisensures that a customer peels the foil 14, rather than trying to removethe whole of the permanently bonded plastic ring 12 from the can body 2.

FIG. 7 shows an alternative container 1 which has a generallycylindrical can body 2 terminating at its upper end with flange or curl6 at the edge of the can body. The ring 12 includes a flat shoulderportion 20 which extends outwardly and downwardly into a retentionportion 22 and upwardly into a rim 24. The retention portion 22terminates in a hooked portion 25 which partially extends underneath theflange or curl 6 to assist in retaining the ring 12 on the can body 2.The ring 12 is permanently bonded to the can body, with the bondedregion including the exterior surface of the curl or flange 6. As can beseen from FIG. 7, in this embodiment the plastic ring 12 does not extenddown along the interior surface of the can body 2, thereby avoiding theneed to provide an expanded portion on the can body. Consequently,release of product from the resulting container is not impeded.

FIGS. 8 and 9 represent an embodiment of the invention in which aplastic ring 30 is bonded permanently to the foil 14. As clearly seenfrom FIGS. 8 and 9, the foil 14 is bonded to the external sidewall ofthe plastic ring 30. The combination of the plastic ring 30 and foil 14is attached to the can body 2 by peelably bonding the foil to the innerwall of the can body 2 around the upper sidewall 32 of the can body 2.The plastic ring 30 incorporates a large ring-pull style of tab 36 forease of gripping when removing the foil (and ring) from the container 1.

1. A container comprising: a metal can body, and a combination of a ringand a foil membrane, the combination being attached to the can body, thering is formed of a material comprising a plastic the inside diameter ofthe plastic ring is no less than the inside diameter of the can bodyaway from the attachment location of the ring on the can body.
 2. Acontainer as claimed in claim 1, wherein the edge of the can body towhich the ring/foil membrane combination is attached comprises anexpanded portion, all or part of the ring locating within the expandedportion, the inside diameter of the ring being no less than the insidediameter of the unexpanded portion of the can body.
 3. A containeraccording to claim 2, wherein the height of the ring corresponds to theaxial length of the expanded part of the can body.
 4. A containeraccording to claim 1, wherein the ring is directly bonded to thesidewall of the can body.
 5. A container according to claim 1, whereinthe ring comprises at least one of polypropylene or modifiedpolypropylene.
 6. A container according to claim 5, wherein the modifiedpolypropylene comprises polypropylene grafted with maleic anhydride. 7.A container according to claim 1, in which the plastic ring is bondedpermanently to the can body and the foil membrane is bonded peelably tothe ring.
 8. A container according to claim 1 wherein the can bodycomprises a curl or flange and the ring comprises a shoulder, theshoulder extending into an outer peripheral wall which depends from theshoulder over the outside of the can body curl or flange.
 9. A containeraccording to claim 8, in which the outer peripheral wall comprises ahook portion which clips over the can body curl or flange to retain thering on the can body.
 10. A container according to claim 1 wherein thering comprises a portion which projects upwardly to provide a rim, thebase of the container and the rim each being formed such that the baseof a first container may be located within the rim of a secondcontainer.
 11. A container according to claim 1, wherein the ring isprovided with a substantially flat bonding surface, and the foilmembrane is bonded to this flat surface.
 12. A container according toclaim 1, wherein the ring is provided with a bonding surface inclineddownwardly at an angle of up to 60°, and the foil membrane is bonded tothis inclined surface.
 13. A container according to claim 1, wherein thering is provided with a bonding surface inclined downwardly at an angleof up to 45°, and the foil membrane is bonded to this inclined surface.14. A container according to claim 1, wherein the foil membrane is cupshaped and the sidewall of the foil cup is bonded to the inner sidewallof the ring.
 15. A method of forming a container, the method comprising:forming a metal can body; fixing a ring formed of a material comprisinga plastic permanently to the can body, the inside diameter of theplastic ring being no less than the inside diameter of the can body awayfrom the attachment location of the ring on the can body; and bonding afoil to the ring such that, in use, the foil may be peeled from the ringfor dispensing a product from the container.
 16. A method according toclaim 15, wherein the can body is formed with a radially expandedportion at one end of the can body, and the plastic ring is fixedpermanently to the can body such that all or part of the ring is locatedwithin the expanded portion.
 17. A method according to claim 15, inwhich the step bonding the foil occurs before the step of fixing thering such that the foil is first bonded to the ring and the combinedring and foil is subsequently fixed to the can body.
 18. A containercomprising: a metal can body, and a combination of a ring and a foilmembrane, the combination being attached to the can body, the ring isformed of a material comprising a plastic, the ring/foil membranecombination comprises a permanent bond between the membrane foil and thering and the foil is peelably bonded to the inside of the can bodysidewall.